This application claims priority to Great Britain Application UK No. 0007800.6 of Mar. 30, 2000, the disclosure of which is incorporated herein by reference.
The present invention relates to a fluid-operated circuit for setting the top dead center and the bottom dead center location of the punch actuation cylinder in punching machines.
Punching machines use different technologies in order to preset the useful strokes of the punch actuation cylinders and accordingly to preset the top dead center (TDC) from which the stroke begins and the bottom dead center (BDC) where the active step of the stroke stops.
Control of the TDC is performed by means of an electric-hydraulic copying distributor which is driven by a fast driver which performs a stroke inside a chamber of its own, under the action of magnetic fields generated by at least one pair of coils which can be excited electrically with intensities varying according to the requirements. The distributor moves in the chamber in contrast with springs arranged at the ends, and drives, thanks to these movements, the opening and closure of the feed and discharge ports of the hydraulic circuit that physically actuates the cylinder of the punching machine.
A first mechanical embodiment for determining the level of the TDC from which the cylinder begins its active stroke and of the BDC comprise mechanical stop elements, in practice axially adjustable pins, on the punching cylinder, or more specifically on a support rigidly associated therewith. Such pins are adapted to abut respectively against a corresponding lower abutment, which is fitted in a fixed position, and the spool of the copying distributor, sliding in the opposite direction with respect to the active and return strokes of the cylinder, and said stop element determines the final stop of its descent stroke (BDC), while abutment against the spool stops the ascent stroke (TDC).
Both pins have manual adjustment, so that they can be arranged micrometrically, as required, accordingly changing the extent of the active stroke.
Another technical embodiment of a digital kind consists in introducing electronic stop elements in the logic controller that controls the movement of the copying distributor; when the dead centers are reached, the stroke of the distributor, and accordingly the active and return strokes of the cylinder, stop.
In both cases, the prior art suffers from drawbacks.
A first drawback linked to the solution with a mechanical stop element is the fact that control of the stroke of the distributor occurs only by acting manually on the adjustments of the stop pins, and evidently causing a waste of time in order to complete the intervention every time it is required.
A second drawback, linked instead to the application of digital stop elements, is the fact that their position cannot be adjusted continuously but can only be adjusted by segments of modular levels which can be gradually added or subtracted. Essentially, it is not possible to perform linear interpolation of the segmented values and accordingly the stroke of the distributor and therefore of the cylinder can only be adjusted and stopped at each individual end of the modular segments and not, if required, between the ends of at least one segment.
Moreover, it is also necessary to be able to control the speed of the stroke of the cylinder. Indeed the control is very important if not indispensable in particular types of application of punching machines, such as for example the provision of a thread in a metal plate.
Finally, when mechanical resistance to full or partial penetration of the metal plate by the punch is high, it is essential to have an increase in the active force of the cylinder available.
The aim of the present invention is to solve the above-mentioned problems of the prior art by providing a fluid-operated circuit for setting the top dead center and the bottom dead center of the punch actuation cylinder in punching machines, and which has none of the drawbacks of the known devices.
This aim and other objects are achieved by a fluid-operated circuit for setting the top dead center and the bottom dead center location of the punch actuation cylinder in punching machines, comprising a first copying means which distributes pressurized fluid, which has a spool at one end and can be connected in output to the upper section of the chamber in which the plunger of the actuation cylinder slides and in input to a first pumping means for feeding low-pressure fluid and to at least one first fast-acting electric valve means, characterized in that said spool is locatable by contact pushing by way of a corresponding means with continuous micrometric movement.